article. In fact, when the aliquot is made up to final volume with ethanol and water, entrapped bubbles appear from time to time on the optical surfaces of the cells. A stirring action is necessary to remove these bubbles, and this effect is achieved only in the titration cell. Thus, the use or distilled water in the reference cell was adopted. For the purposes of calibration, synthetic standards were made up from phosphoric acid and standard sulfate solution to cover the range from 0 to 77& The use of synthetic standards has the advantage that the final results on the assays are not dependent on the accuracy of gravimetric determinations. The calibration graph obtained appears to he linear over the range investigated, and the reaction between titrant and sulfate ions is, to all intents, staichiametric. Samples of process acid made from Figure 1. Stirring device and cuvette Nauru rock were analyzed by this method, and the results obtained were in ( to the original close agreement to those obtained by the classical gravimetric procedure. Re. p r o c s u u ~W~Z L C LLLC u s of a green filter in t h e rolorimrtcr., 2nd t h e tcchninllp sults of tests bv the authors showed that ~~.~~~~~ 7:the method is tolerant of impurities of setting to zero using distilled water m found in wet-process acid. The calcium the second cell. It was considered that oxide, fluoride, iron oxide, and alumiany errors, owing to the dilution by num oxide contents can vary over a titrant of the background color in the wider range than would he normally process acids, would be minimized by encountered, without any significant using a green filter rather than a colorless effect on the results of the sulfate determatt filter. I n actual practice: this final mination. The results are also inbackground is slight, but varies (in independent of the phosphorus pentoxide tensity and color) with the origin of the contents of the filtrate acid. phosphate rock used in the process. I n the early stages of the study, This possible source of error is not some work was done using proteceliminated by the use of a second aliquot tive agents, not to achieve reproin the reference cell, as in the Russian ~~
~~~~
~~~~~~~~~~~~~
ducible particle size hut to minimize layering effects a t the higher ranges. Use of these agents is necessary for turbidimetric measurements where absorbance is related to sulfate content (7, 2, 6 ) , but as pointed out earlier, this method does not depend on reproducible particle size. The early work showed that, with the stirrer design and speed used, no advantage was gained by using these protective agents, and accordingly their use was not incorporated in the method.
Acknowledgment The authors acknowledge the encouragement and advice of I. 0. Horys , Chief Chemist, and thank the Manas;ement of Sulphide Corp. Pty., Ltd., and 1S e e n leaf Fertilizers, Ltd., for permiss;ion to publish this paper. . .
Precipitated Impurities in Fertilizers Prepared from Wet-Process Phosphoric Acid
~
~
(1) Bentata, A., I.C.I.A.N.Z., Melbourne, private communication, 1965. M. L., Makarevich, (2) Chepelevetskii, V. M., Zovodsk. Lob. 30 (8), 935 (1964). (3) Claudy, H. N., Karasek, F. W., Ayers, B. O., Skinner, J. G., Anal. Chem. 31,1255 (1959). (4) Gassner. K., Friedel, H., Z. A n d . Chem. 152,420-4 (1956). (5) Nelson, G., PTUC. Fertilizer ,Sot. 79, 30 (1963). ~-, (6) Puschel, R., Lassner, E., ChernistAna(vst49, 90 (1960). ~~
~~~
~~~~
I M P U R I T I E S F R O M PHOSPHORIC ACID
; cjred ~
L
~
~
\-.
Received for review Jonuory 3, 7966. Accepted April 2, 7966.
I
A. WILLIAM FRAZIER, JAMES P. SMITH, and JAMES R. LEHR Division of Chemical Development, Tennessee Volley Authority, Wilson Dam, Ala.
Ammoniation of wet-process phosphoric acid precipitates the metallic elements that were dissolved from the phosphate rock or added as micronutrients. The nature and solubility of the precipitates change as the acid is concentrated to the superphosphoric acid range and condensed phosphate species are introduced. The optical properties and x-ray patterns of 26 of the most common precipitates are described.
w.
phosphoric acid cant a m soluble impurities, mostly iron and aluminum, that were dissolved from the gangue minerals in the phasphate rock from which the acids were prepared. In the concentration of these acids to merchant-grade (24% P, 54% PzOS)or superphosphoric acid (about 3370 P, 7S% P * 0 6 ) , some of the impurities precipitate during storage as ,.. campounas, (Y ,"\ , , crysralnne j tnat interrere seriously with mechanical handling of the acid and immobilize some of the ET-PROCESS
.
522
J. A G R . F O O D C H E M .
phosphate. Considerable amounts of these impurities-iron, aluminum, calcium, and magnesium-remain in solution or as suspended solids, particularly when additives are introduced during production of the acid to stabilize suspended solids or delay their formation until the acid is processed into other fertilizers. The preparation of fertilizers from wet> , . .. usually ,, enrails . ., process pnospnoric acia ammoniation of the acid; the acid or its ammoniation product often is concen-
trated, and many of the products thus contain condensed phosphates as well as orthophosphate. Addition of salts of potassium to prepare complete fertilizers and of micronutrients increases the amount of metal cations that may take part in precipitation processes. The change in pH during ammaniation and the introduction of condensed phosphate species by concentration steps ,. in . precipirarion . .. .. or me aissoivea 1. I ~I resuir metallic impurities; these crystallization processes usually require an induc/.
..
~
~
tion period of several days and may be accelerated by temperature changes during storage of ):he product. Unammoniated, concentrated acids yield precipitates that are mainly orthophosphates or tripolyphosphates ( 9 ) : but the precipitates in ammoniated concentrated acids are mainly pyrophosphates. The identification and characterization of precipitated impurities isolated from a wide variety of experimental fertilizers prepared from ammoniated wet-process phosphoric acids are reported here. Some of these compounds have been identified previously as products of the reaction of phosphates with soil minerals (7, 70) but many of the compounds have not been reported bs-fore or have been incompletely charactrrized. I n addition to the metallic impurities in phosphoric acid and added micronutrient metals such as zinc, manganese, and copper, impurities are added by corrosion of process equipment, such as ferrous iron if the processing equipment is mild steel. The micronutrients, like the metallic impurities, form insoluble phosphates which alter ):he rates a t which the micronutrients become available to plants in the soil. 1.n liquid fertilizers, the precipitates settle out with resultant segregation of micronutrients and interference with mechanical handling of the solutions. Because of the wide variations in conditions under which ammonium polyphosphate fertilizers are prepared, no attempts were made to determine the solubilities of the coinpounds in any of their mother liquors The amounts of precipitates that form in the preparation of a solid or liquid fertilizer depend on so many variables-composition of the acid: amounts of other fertilizer salts added, temperature attained during ammoniation, etc.-):hat no generalizations can be made about the difficulties the precipitates will introduce in subsequent use of the feriilizers. The information presented here is intended to assist fertilizer producers in identifying the undesirable solid phases in their products so that means may be devised to prevent their formation. Many of the compounds reported here occur in fertilizers in particle sizes too small for detailed o:?tical characterization. These compounds were prepared also in the 1aborai.ory from reagent chemicals under conditions resembling those in Ivhich they were formed in the production of the fertilizer material but which yielded well cr vstallized products. The laboratory preparations, whose optical properties agreed with those determined on the materials isolated from fertilizers, Ivere used for measurements of the optical and crystallographic properties of the compounds. During the preparations, other salts of related composition were sometimes obtained that were not found in fertilizers ; their ~
properties are reported also, since they were formed under conditions that may be encountered in the ammoniation of different concentrations of wet-process phosphoric acid. Most of the laboratory preparations were made a t room temperature by adding a soluble salt of the metal to a saturated solution, prepared from reagent chemicals, of ammonium phosphates similar to the fertilizer solution in \vhich the desired compound had been observed. Most of the compounds precipitated rapidly, and addition of the soluble metal salt was continued only until the amount of precipitate was sufficient for optical and x-ray examinations and for chemical analysis. Two compounds, however, required a different method of preparation. The compound Fe(NH4) 3HP04P2O7 was prepared from a mixture of 2 grams of FeP04 and 15 grams of ammonium polyphosphate that contained 14% N and 26Tc P (607, P2Oj) and in vhich half the phosphorus was ortho- and half pyrophosphate. The mixture was heated in a sealed glass tube a t 230’ C. for 1 to 2 hours; the cooled product was washed with Ivater to remove the excess ammonium phfxphate. washed briefly with acetone. and air dried. Members of the series (A1.Fe)XH4P2Oi Xvere prepared similarly from mixtures of 2 grams of the appropriate mixture of Alp04 and FeP04 and 15 grams of the same ammonium polyphosphate. T h e mixtures were heated in sealed glass tubes a t 250’ C. for I 6 hours, and the cooled products were washed and dried as above. Complex phosphates, such as those discussed here, usually dissolve incongruently in water or any solvent that differs significantly from the mother liquors in which they were formed. Most of these compounds are very slowly soluble, however, and the adhering mother liquor was washed off trithout detectable decomposition of the compounds. The methods of chemical analysis were the same as those used in the study of the precipitates in wetprocess phosphoric acid ( 9 ) . The compositions of the crystalline compounds are listed in Table I, their optical properties and morphology are described in Table 11, and their x-ray powder diffraction patterns are shown in Table 111. The compounds listed in the tables either have not been reported previously in the literature or have been incompletely characterized. Calcium Salts
[Vet-process phosphoric acids usually contain small amounts of calcium. In the ammoniation of acids that contain no condensed phosphates, calcium precipitates as Calo(POa)6(OH,F)2 (apatite), C a H P 0 1 . 2 H 2 0 ,or as the dimorphs ofCa(NH4)?(HP04)2 HzO ( 4 ) . VOL.
In more concentrated acids (about 337c P, 7 3 4 P z 0 6 ) that contain about equal amounts of ortho- and pyrophosphate, ammoniation to p H 4 to 6 precipitates calcium as Cas(”?) z(Pz0;) 2 . 6 H 1 0 ; above p H 6, Ca(NHi)ZP20;.HzO is precipitated (7, 2). In still more concentrated acids that contain considerably more pyro- than orthophosphate, Ca(XH4)4H?(P2Oi)z is precipitated a t p H 4 to 6. The formation of calcium salts in ammoniated wet-process acid is not a major problem, since most wet-process acids contain a n excess of sulfate over that required to combine with the calcium as calcium sulfate, and only a small amount of calcium remains dissolved in the acid. Magnesium Salts
LVet-process acids frequently contain magnesium dissolved chiefly from dolomite in the phosphate rock; magntsium also is added to liquid fertilizers as a secondary nutrient and in attapulgite clay, a stabilizing agent. Ammoniation of merchant-grade acids (22-24y0 P, 50-547, PLOI) precipitates magnesium as M g N H 1 P 0 4 6 H n 0 (struvite) or its monohydrate, depending on the temperature and sometimes as Mg,(NH4)?H 4 ( P 0 4 ) 48 H r 0 (hannayite) and Mg( N H 4 ) 2 H 2 ( P 0 4 )4LH 2 0 ( 3 ) . [\’hen potassium is present. magnesium may precipitate as MgKPO4 6 H z 0 (7.1) which is isomorphous \\ ith struvite. If aluminum is present, magnesium precipitates as hlg.41(NH4)6H?(P04)4 6 H z 0 , a salt frequently found in ammoniated merchant-grade wet-process phosphoric acid; and in ammonium polyphosphate liquid fertilizers prepared from wet-process phosphoric acid ; its iron analog has not been observed. O n ammoniation to p H 3.5 to 6.0 of solutions of orthophosphoric and pyrophosphoric acids that contain magnesium, the magnesium precipitates preferentially as pyrophosphate, the monoclinic dimorph of Mg(NH4)2P207 4 H z 0 in highly concentrated solutions, and the orthorhombic dimorph in less concentrated solutions. I n solutions that contain more ortho- than pyrophosphate, as in most ammonium polyphosphate liquid fertilizers, the orthorhombic dimorph precipitates from concentrated solutions. In ammonium pyrophosphate solutions with p H above 6, magnesium precipitates as Mg(NH4)6(P20 7 ) 2 6HzO and in those with p H 2 to 3, as Mg(XH4)2H4(P20i)2. 2H2O. Precipitated magnesium compounds are a source of considerable trouble during storage and handling of liquid fertilizers prepared from ammoniated wetprocess phosphoric acid. The salts are quite insoluble, but tend to supersaturate and precipitate slowly over several days or weeks, forming large, well developed plate or acicular crystals that
1 4 , NO. 5 , S E P T . - O C T .
-
1966
523
Table I. Solids in Ammoniated Concentrated Wet-Process Phosphoric Acid Comporifion, Weight
Compound
Ca(“4 ) ~ H P?Oi)s z( Stoichiometric MgNH4P04. H20 Stoichiometric MgKP04.6HzO
Stoichiometric Mg(NHa)2P20?.4H*O I Ma(hH4)ePs07,4H20 I1 ”. Stoichiometric MgL41(NH4)SH?(P04)4. 6H20
Stoichiometric Al(KH4)sPzOiOH.2H20 Stoichiometric A 1 0 . d e 06WW”Oi . Stoichiometric Alo.jFeo.SKP20i Stoichiometric Fe( NH4)3HPO?P207 Stoichiometric Fe(NH4)3HP0?P2O7. H20 Stoichiometric Fe(NH4)dP207)2. 6H2O
Stoichiometric Fe(NH4)YP2Oi.2H20 Stoichiometric
Mn(NH4)2P207.2H20
Stoichiometric ZnNHdH3(P04)2.H20 Stoichiometric ZnNH4P04 .4 ZnNHaP,Oa B Stoichiometric Zn2KH(PO11 2 Stoichiometric
Ca, Mg, Fe, Mn, or Zn
8.93 8.66 15.32 15.74 9.23 9.13 5.31 5.43 3.98 4.13 7.86 7.78 7.94 3.80 4.01
...
14:04 15.65 9.29 10.79 14.33 14.74 13.96 14.04 8.39 8.87 17.64 18.50 17.74 18.27 21.49 22.21 36.4 36.32 36.67 36.07 36.32 31.98 32.94 32.70 32.79 13.40 13.59 10.04 10.39 22.42 22.29 30.69 31.82
are difficult to pump or handle in distributor equipment.
Zinc Salts Zinc, an increasingly important micronutrient, is sparingly soluble in many phosphatic liquid fertilizers. \Vhen a soluble zinc salt is added to ammonium orthophosphate solutions, the zinc forms supersaturated solutions and precipitates as ZnNH4H~(P04)2.H20a t p H 3, as the hexagonal dimorph of ZnNH4P04 a t p H 3.5 to 5.5, and as the orthorhombic dimorph of ZnXHdPO4 a t p H 6 and above. Zinc added to potassium orthophosphate solutions precipitates a t p H 4 as ZnzKH(PO4)2,2H20 (which slowly dehydrates in the mother liquor to the anhydrous salt), and as ZnKP04 a t p H 5 to 7. Hopeite, Znr(PO4)n .4H20, has not been found in high-analysis ammonium or potassium phosphate fertilizers, but it
524
J. A G R . F O O D C H E M ,
70
MoleslMole P
HsO AI
N or K
P
(diff. )
... ... ... ... ...
11.74 11.58 8.88 9.05 13.77 14.65 6.30 6.25 13.84 14.27 9,05 8.99 9.14 10.93 11.42 9.69 9.65 5.82 5.87 15.18 15.03 10.82 11.04 10.39 10.55 13.68 13.34 8.78 9.28 9.15 9,30 4.77 4.75 7.75 7.81 7.85 11.20 10.79 9.96 9.79 19.80 19.61 5.71 5.82 13.6 13.35 9.35 9.54 4.58 4.54
26.42 26.85 19.95 20.08 11.75 11.64 27.16 27.68 21 ,Os 21.09 20.26 20.08 20.22 19.78 20.22 21.44 21.38 25.85 26.02 24.58 23.89 23.99 24.45 23.27 23.36 20.02 19.68 20.17 20.54 20.65 20.60 20.87 21.05 17.33 17.33 17.38 17.25 17.20 15.46 15,63 15.63 15.55 25.19 25.76 19.93 19.70 20.98 21.13 20.35 20.13
5.2 3.9 12.4 11.1 41.2 40.6 17.3 16.1 19.5 18.4 23.8 24.4 23.5 20.2 20.0 14.9 15.5 3.8 0.0 4.2 0.0 4.4 2.4 7.4 6.8 17.9 17.1 14.8 11.9 12.8 12.0 16.6 15.3 0.6 0.6 0.0 2.1 2.5 12.8 11.3 -0.3 0.0 15.0 13.3 16.6 17.2 6.7 6.1 6.7 5.8
...
... , . .
... ... , . . , . .
... 4.18 4.40 9.53 9.31 3.23 3.77 4.18 5.20
... ... ... ... ... ,.. , . .
... ... ... . . . . , . .
... ... , . .
... ... , . .
... ...
... ... , . .
...
...
...
... ...
forms over a wide p H range in diluted fertilizer solutions and in superphosphate fertilizers to which zinc oxide has been added. Although hopeite is highly insoluble, it is an effective source of zinc for plants, particularly when it is finely divided (76). Zinc added in excess to solutions of ammonium polyphosphate precipitates as Zn(NH4)2H4(P20i)2 2H20 at pH’s below 4, as Znz(NH4)?(PzOi)? 2H20 a t p H 4 to 6, and as Zn(NH4)2P20i HZO a t p H 6 to 8. The solubility of zinc in concentrated ammonium polyphosphate solutions LLith pH’s of 6 and above increases markedly with increase in the ratio of pyro- to orthophosphate. In concentrated ammonium pyrophosphate solutions with pH’s of 6 and above. a solution saturated with zinc has a mole ratio of Zn to P205 of about 0.5, and this ratio must be exceeded before a zinc salt will crystallize. L‘nder these conditions, zinc crystallizes as Zn(KH4)G-
Cot Mg, Fe, Mn, or Zn
0.26 0.25 0.98 1.oo 1.01 1 .oo 0.25 0.25 0.25 0.25 0.50
0.50 0.50 0.25 0.25 ... ... 0.30 0.33 0.21 0.25 0.33 0.33 0.33 0.33 0.23 0.25 0.49 0.50 0.49 0.50 0.49 0.50 1 .oo 0.99 1 .oo 0.99 1 .oo 0.98 1.00 0.99 1.00 0.25 0.25 0.24 0.25 0.51 0.50 0.72 0.75
AI
N or K
...
0.98 1 .oo 0.99 1 .oo 0.93 1 .oo 0.51 0.50 1.46 1.50 0.99 0.99 1 .oo 1.22 1.25 1 .oo 1 .oo 0.50
... ... ... ... ... ... ...
... ... ...
... ...
0.24 0.25 0.51 0.50 0.14 0.17 0.20 0.25 ,..
... .. ... ,..
... , . .
... ... . . .
... , . .
, . .
... ... ...
... , . . , . .
... . . . , .
. . ... ... ... ... ...
0.50 0.49 0.50 1 .oo 1 . 00 0.99 1 .oo 1.51 1.50 0.96 1 .oo 0.98 1 .oo 0.51 0.50 0.99 1 .oo 1 .oo 0.52 0.50 0.51 0.50 1 .oo 1.00 0.50 0.50 1.52 1.50 0.99 1 . 00 0.50 0.50
Hz0 0.34 0.25 1.07 1 .oo 6.05 6.00 1.10 1 .oo 1.59 1.50 2.02 2.09 2.00 1.76 1.75 1.20 1.25 0.60 0.00 0.60 0.00 0.32 0.17 0.55 0.50 1.54 1.50 1.26 1 . 00 1.07 1 .oo 1.37 1.25 0.06 0.06 0.00 0.21 0.25 1.43 1.25 -0.03 0.00 1.03 1 .oo 1.43 1.50 0.55 0.50 0.57 0.50
(P?Oi)2.6H20, but this salt is congruently soluble in water and would not be a troublesome constituent of a fertilizer. Measurements of solubility in the system NH3-Zn0-H4P207-H20 are being prepared for publication ( 7 7). Unlike calcium and magnesium, which selectively precipitate as pyrophosphates from solutions of any concentration that contain both ortho- and pyrophosphate, zinc precipitates as Zn3(NH4)2(PzOi)2. 2H20 from a concentrated (25% or more) ammonium polyphosphate solution and as ZnNH4PO4, dimorph h, when the same solution is diluted. Manganese Salts
The behavior of manganese in liquid fertilizers was studied only briefly. In the amounts usually added as a micronutrient, trivalent manganese remains dissolved in ammonium polyphosphate solutions. Divalent manganese. how-
Table II. Morphological and Optical Properties Refractive Indices
Crysfal System, Closs, and Habit
Monoclinic, 2/m. Highly modified prisms tabular on (100) MgNHaP04. H20
Orthorhombic, mmm. Plate crystals containing Y-Z elongated along Z Orthorhombic. hemimoruhic. mm. Prisms exhibitigg '(001 ), p;omi;lent (OOT), (101), (101), (Oll), and (011) Triclinic, 1. Rhombic prisms and tablets with contact and polysynthetic twinning Monoclinic, 2/m. Prisms tabular on (loo), modified by ( l l O ) , ( O l O ) , and 1111/ Orthorhombic, hemimorphic, mm. Blades tabular on X-ITplane Monoclinic, 2 / m . and (100)
Mg.Al(NH,)~H~(PO,),. 6H2O .\l[NHi)iPrO,OH. 2H20 AloaaFeoB7NH4P20i
Plates tabular on (010)
Needle to blade crystals, bvith orthorhombic or higher symmetry Crthorhombic. Thin needle crystals Monoclinic, fusiform aggregates of small needle crystals Monoclinic, 2/m. (100) tabletsmodified by ( l l l ) , ( l i l ) , and (111)
(m),
Fe( NH 4 ) 3HP04P20i
Orthorhombic. mmm. containing X - Z
Needles and blades
Orthorhombic, intergrown blade crystals tabular on IT-,?
Fe(h-H4)2P40i. 2Hp0 Mn(NH4)2P20i.2 H 2 0 ZnNH4H3( P04)2.H a 0 ZnNH4P04 A ZnNHdP04 B Zn?KH(P04)?
Monoclinic, 2:m. (100) tablets modified by ( O l l } , j l l 0 ] , a n d s m a l l ( l 0 l ) , (101), and IllO) Hexagonal. rosette aggregates of interpenetrated blade crystals Hexagonal, interpenetrated blade crystals tabular on (0301) Triclinic, 1. Highly modified tabular crystals Orthorhombic, mmm. Prisms tabular on X-Y plane; Y-Z view shows pseudohexagonal symmetry Hexagonal, 62. Bipyramids and rod crystals Triclinic, 1. Highly modified rod crystals Triclinic, 1. Rhombic tablets
ZnKP04
Hexagonal, 62. Needle crystals
Zn(NH4)2H4(PrOi)?.2 H 2 0
Triclinic, 1. Plates containing X' and Z'
Monoclinic, 2 / m . Prisms tabular on (100) with prominent (110) and smaller (OllJ
Orthorhombic, scalar blades tabular on Y-Z plane, elongated along Z Orthorhombic needles and blades
a
Calculated values fix 2V are in parentheses. Calculated from 2V mrasiirement.
1.538 1.558 1.565 cy = 1.549 = 1.569 -/ = 1.571 CY = 1.477 /3 = 1.481 -1 = 1.487 cy = 1.487 p = 1.502 y = 1.522 cy = 1.497 /3 = 1.501 -/ = 1.504 CY = 1.5005 /3 = 1.502 -/ = 1.504 cy = 1.488 p = 1.502 -, = 1.503 Ni = 1.486 N2 = 1,488 cy = 1.490 */ = 1.500 cy = 1.648 /3 = 1.662 */ = 1.677 cy = 1.593 /3 = 1.601 = 1.612 cy = 1.58' p = 1.590 = 1,630 CY = 1.551 p = 1 577 "I = 1 ,600 CY = 1.510 p = 1.51461 y = 1.515 E = 1.556 w = 1.598 B = 1 541 w = 1.581 01 = 1.518 p = 1.521 y = 1.541 cy = 1.582 = 1.589 -/ = 1.591 E = 1.586 w = 1.589 cy = 1.515 p = 1.524 y = 1.546 CY = 1.536 = 1.541 y = 1.548 e = 1.553 w = 1.574 CY = 1.507 p = 1.516 -y = 1.540 = p = y =
CY
-, -,
1.507 1.513 1.514 cy = 1.567 = 1.600 -/ = 1,606 cy = 1.593 p = 1.596 y = 1,601 = = y =
cy
p
Optical Propertiesa
Biaxial ( - ) ,
2V = 60" (060.5'). OAP ,XAc = 53 in acute 8. p = 107.5 , b = 2, d. = 2.05 Biaxial ( - ) , 2V = 40' (35'). O A P 1 tabular plane, Z I] elongation. d. = 2.15 Biaxial (+), 2V = (78"). 0.4P = (OOl), X = b , Y = c, Z = n. d. = 1.91 J- ( O l O ) ,
Biaxial ( f ) , 21' = (8Z3). d. = 2.01 Biaxial ( - ) , 2 V b =
(75').
O.\P
=
(OlO),
Y,Z A G = 40' in obtuse p.
=
=
107',d. = 1.66 Biaxial ( + ) , 2 V = 75" (82"). O A P l tabular plane, X 1; rlongation. d. = 1.79 Biaxial ( - ) , 2V = 33" ( 3 0 " ) . 0.4P = ( O l O ) , b = I , Z A c -16" on (010) in = 120", d. = 1.77 acute 6. Parallel extinction, X 1 elongation. d. = 1.78 Z 1; length, d. = 1.84 Biaxial ( f ) , 2V = (89'), Z almost length. d. = 2.64 Biaxial ( f ) , 2V = (82'). OAP b = Y.d. = 2.89
=
(OlO),
Biaxial ( + ) , 2 V = ( 3 0 ' ) . OXP = plane of tabularity, Z 11 length. d. = 2.14 Biaxial ( - ) . 2V = (85"). O.\P 1 tabular plane, Z ,I length. d. = 2.01 Biaxial ( - ) , 2 V = 25'. 0.AP I ( O l O ) , X'Ac = 43" in obtuse 8. b = Z. d. = 1.75 Uniaxial ( - ) . d = 2.24 Uniaxial ( - ) .
d. = 2.17
Biaxial (+), 2V
=
39" (43').
Biaxial (-), 2V = 45'[50"). tabular plane. d. = 2.54
d. = 2.29
OAP
Uniaxial ( - ) .
d. = 2.54
Biaxial (+), 2V
=
70" (67').
Biaxial (+), 2V
=
80" (81"). d.
Uniaxial ( - ) .
I
d. = 2.99
=
2.83
d. = 3.25
Biaxial (f), 2V = 60' (63'). OAPA length = 15 ', and inclined to plate by 37"; X A length = 15", and-inclined to plate by I " . d. = 2.16 Biaxial ( - ) , 271 = 40' (45"), 0 . i P 1 ( O l O ) , Y A ,= 47"in acute 9. b = Z, p = 108 . d. = 1.77 Biaxial ( - ) , 2V = (45"). O.\P 1 plane of tabularity, Z !' elongation. d. = 2.42 Biaxial ( f ) , 2V = (85"). X I/ length. d. = 2.85
A11 values for densities are calculated by the Gladstone-Dale equation (8).
V O L . 1 4 , NO. 5, S E P T . - O C T .
1966
525
Table Ill. d, A.
I
10.09 5.38 5.24 5.06 4.70 4.39 4.21 4.16 3.57 3.35 3.31 3.28 3.18 3.12 3.07 3.05 2.93 2.78 2.76
2 53 2 41 2 37 2 20 2.17 2.13 2.08 2.05 2.03 1.932 1.887 1.861 1.819 1.776 1.760 1.726
7 8 7 13 4 4 5 5 7 3 4 3 4 4 4 4 4 4
MgNHaPOa. H20 100 1.994 29 1.878 2 1.853 24 1.823 4 1.785 4 1,754 1 1 ,728 3 1.674 2 1.619 42 1,581 50 1.554 19 1,537 8 1.515 5 1.497 11 1.485 9 1.461
2 8 4 3 3 5 4 10 6 3 2 2 1 2 8 3
17 100 35 5 10 11 13 26 13 12 39 12 10 9 8 14 8
8.77 4.72 4.38 4.20 3.64 3.45 3.36 3.23 3.10 2.92 2.80 2.50 2.40 2.33 2.28 2.12 2.04
5
5.84 5.54 5.37 4.58 4.23 4.12 3.54 3.44 3.25 3.16 3.08 3.00 2.97 2.90 2.81 2.77 2.72 2.69 2.64 2.53
16 82 35 18 100 100 9 15 52 13 12 9 32 53 10 89 15 96 42 10
2.51 2.37 2.33 2.24 2.11 2.05 2.04 1.997 1.968 1,947 1.926 1 ,849 1,796 1.763 1.737 1,715 1.631 1.585 1.543
20 15 15 10 7 11 8 18 14 20 12 8 24 14 14 10 6 10 6
Powder X-Ray Diffraction Patterns“ I d, A. I M~(NH~)~H~(P~O;)P.~HZO 3.02 30 1.737 7 2.992 12 1.731 5 2,861 7 1.704 4 2.815 5 1.673 4 2.774 12 1.661 4 2.654 16 1.623 5 2.580 21 1,602 4 d, A.
8.63 8.07 7.81 7.22 6.53 6.18 5.96 5.34 5.04 4.99 4.94 4.84 4.65 4.45 4.32 4.18 4.04 3.96 3.91 3.50 3.32 3.28 3.22 3.16 3.10
Mg(NH4)dP20,)2.6H2O 24 3.05 14 2.99 55 2.98 27 2.93 72 2.78 37 2.66 6 2.63 100 2.60 7 2.59 9 2.53 11 2.45 5 2.36 13 2.32 20 2.27 26 2.19 5 2.172 15 2.167 12 2.093 6 2.066 18 2.017 59 1.974 9 1.849 22 1.821 24 1.806 12 1.603
Mgl:KHa)pPpOi. 4 H p 0 3 2.439 8.26 100 2,385 7.47 54 2.365 6.27 12 2.289 6.09 31 2.219 5.78 43 2,204 5.39 10 2.158 5.28 5 2.141 4.89 4 2.099 4.58 11 2.090 4.44 4 2.071 4.31 2 2.033 4.13 5 2.006 3.81 79 1.965 3,74 18 1.947 3.56 16 1.918 3.52 6 1,900 3.43 18 1.870 3.24 9 1.854 3.19 13 1.810 3.16 3 1.800 3.11 15 1.763 3.05 35 1.750 2.930 24 1.715 2.897 10 1.684 2,825 15 1.660 2,761 E 1.651 2.712 13 1.618 2.656 16 1.595 2.641 14 1.588 2,494
9 35 39 52 T
4 5 6 9 11 9 6 6 8 9 10 18 3 9 4 5 5 5 5 6 3
9 2 16 3 3 3 2 5 3 3 2 8 6 2 4 3 11 2 2 5 9 3 3 3 2 3 2 3 3
Mg(‘ N H ~ ) ~ H ~ ( P z2OH,p) 0. 28 2 477 6 7.28 10 6.58 53 2.431 13 10 2.400 5.94 84 2.355 4 5.55 4 6 2,327 5.32 Mg( NHa)2Pp07,4Ha0 5 100 2.203 4.80 3 60 2,421 4 4.36 4 2.181 6.30 2 53 2,399 4 2 I62 8 5.96 4.25 . . ~ 4 4 4.08 5.22 5 2.124 2 7 4.63 3.64 88 2.106 6 4 4.01 79 2,071 3.62 2 4 3.57 22 1.984 3.53 2 6 3.55 42 1.938 3.45 3 6 3.46 29 1.892 3.29 7 4 3.37 35 1.849 3.19 3 5 3.20 3.16 10 1.811 4 16 1.993 4 3.16 3.07 13 1.755 4 4 1.982 3.11 5 12 1 ,743 3.06 Intensities a Patterns obtained with an x-ray diffractometer, CuK, radiation, A = 1.5405 A. ground and expressed as per cent of strongest line. ~~
~
526
J. AGR. F O O D C H E M .
d, A.
I
d, A.
Mg(T\”4)2P20;.4H20 I1 2.970 7 1.966 2.930 2 1.940 2.877 16 1.865 2.832 5 1,821 2.685 4 1.787 2.677 4 1.778 2.663 5 1.773 2.614 4 1.723 2.583 13 1,603 2.553 1 1.573 2.510 2 1.560 2,449 1 Mg41(SH4)5H2(P04)46HpO 8 72 87 2 74 8 31 3 2 73 7 42 100 2 68 7 03 8 2 58 6.44 4 2 52 6 10 12 2 48 5.49 43 2 45 5 00 5 2 42 4.51 6 2.38 4.27 5 2.33 4 18 4 2.32 4.11 2 2.29 3.72 3 2.23 3.65 7 2.15 3.53 9 2.14 3.49 2 2.04 3.30 2 1.970 3.24 8 1.953 3.19 8 1.933 3.15 28 1.906 2 99 10 1 865 2 95 15 1 827 2.90 7 1 768 2 88 5 1 751 2 81 5 1 653 2 ’8 5 .L\lINHa)zPzO,OH 2 H 2 0 100 2 817 8 10 18 2 748
9 46
6.21 5 63 -5 . 13 .4.91 4.75 4.40 4.15 4.03 3.92 3.86 3.75 3.56 3.50 3.39 3.30 3.17 3.13 3.06 2.902 2.857
4 65 43 19 3 4 6 10 3 3
4 17 19 10 8 6 10 39 33 26
2 538 2.497 2 412 2.326 2.245 2.194 2.098 2.011 1.981 1.925 1.877 1.837 1.810 1.778 1.752 1.704 1.652 1.624 1.568
Al0 33Fe0.67NH4P~07 5.82 100 2.98 5.29 31 2.95 4.96 11 2.92 4.17 11 2.63 3.95 61 2.48 3.41 12 2.42 3.12 17 1.98 3.09 12 1.75 3.00 38 measured as peak heights above
2 5 2 4 4 2 2 2 5 3 2
6 9 6 4 2 3 7
2 6 3 5 5 3 3 4 3 3 2 2 2 3 2 3 2 2
-
22
8 16 6
5 4 15 12 5 9 4 5 3 4 3 3
3 4 5
44 62 10 12 7 21 7 15 back-
Table 111. d, A.
5.74 5 24 4.19 3 92 3.64 3.52 3.38 3.24 3.08 3.04 2.99 2.95 2.92
d, A.
I
.Alo.:Fell,~KP2, 54 2.61 13 2.47 16 2.41 46 2.38 11 2.28 11 2.26 26 2.19 6 2 13 26 2.09 13 2 04 35 2 03 1 96 40 1 72 100
d, A.
I
15 8 7 18 9 9 9 11 15 11 9 12 15
Fe(NH4) , H P 0 4 P ? O j 2.94 2.92 2.88 2 ’8 2 76 2 67 2 01 2.51 2.31 2.25 2.14 2.03 1 ,968
7,85 7 31 6,58 5.13 4.67 4.06 3.94 3.68 3.50 3.45 3.39 3.30 3.22 3.12 3.07 3.01 2.97
100 33 59 12 6 10 8
5 19 15
1 862 1.776
8.29 7.64 5 19 4 68 4 5’ 4.35 3.92 3.87 3.81 3.71 3 50 3 43 3 24 3 05 3 02 2 95 2 92 2 88
64 100 12 15 7 6 12
2.83 2.77 2 66 2 62 2 59 2.53 2.50 2.23 2.17 2.15 2.12 2.10 2 09 2 03 1 94 1 86 1 79
3
15 16 8 15 3 C
T
3
14 12 21 10 14 15 5 6 9
1I
0/ 1I d:
10 8 5 6 4 4 13 4 6 3
4 4 3 C
8 12 6 6 4 6 3
5 3
5 5
9.24 7.47 4 80 4.70 2.79
100 23 26 13 21 3 4 17 3 6 5 11 17 4 4 10 18 9
47 100 38 53 69
2.93 2.80 2.67 2 61 2 59 2.52 2.50 2.45 2 31 2.26 2.24 2.22 2.19 2.17 2 13 2 10 2 07 1.85
24 7 2 3 3 3 3 3
3 3
d, A.
d, A.
I
Mn(NH4)2P2O7.2 H 2 0 94 100 30 30 48 58 ZnNHdHa( PO4)2. H?O
7.18 6.88 6.61 5.97 5 64 5 24 5 02 4.76 4.16 3.99 3 91 3 70 3 60 3 55 3.43 3 32 3.20 3 08 2.99 2 88
4 5
Fe(SH4)6(I)2O7)2.6HsO 8.70 7.82 6.57 6 16 5 34 4.64 4 48 4 36 4.08 4.03 3.96 3.52 3.34 3.22 3 16 3 04 3 01 2 9’
7.80 7.47 6.20 4.89 4.76 2,83
Continued
I
100 6 4 88 74 8 4 2 6 13 2 5 24 8 6 41 6 10 2 7
2.82 2.75 2.69 2.66 2 62 2 55 2 51 2.50 2.44 2.40 2 29 2 20 2 12 2 004 1.991 1.883 1 861 1 847 1 799 1 773
4 6 7 7 8 7 7 5 2 6 3 2 5 9 5 5 5 6 3 7
Z n N H 4 P 0 4 .\ 9.24 8 91 6 27 5.14 4 65 4.47 4.38 4.10 3 98 3.93 3.46 3.42 3.21 3.20 3.14 3.12 2 98 2 78 2.72 2.67 2.62 2 55 2.50 2.48 2.46 2.44 2.31
5 4 64 3 100 48 73 8 6 6 7 8 62 52 19 21 13 27 56 11 57 4 21 11 7 4 4
2 24 2.20 2.17 2.13 2.0‘ 2 04 2.01 1,990 1.945 1.877 1.827 1 ,779 1 ,745 1 736 1.718 1 688 1 679 1.660 1 641 1.625 1.612 1 ,607 1,590 1.569 1.564 1 550
30 3 5 2
20 4
4 7 4 3
7 17 13 6 9 4 3
65 2 3 66 86 29 6 7 4 36 100 23 2
-3. 46-
2.28 2.23
11 5 3 3 7
15 2 3 8 5 7 17 3 5 15 13 3 17 10
I . 6L8
1.31
2.55 2.52
2.17 2.12 2.04 2 01 1 964 1 921 1.907 1 846 1 808 1 7’8 1 749 1 713 1 686
11 7 78
_I
10 27
1.623 1.585 1 . -458 ” 1 5 A11 ~
I
.I
VOL.
14
I
5 5 4 16 4 4 6 21 3 3 7 4 9 9 4 11 4 5
Zn2KH(POl)i 2H20 12 87 8.15 7.74 7.66 7.46 6 67 6 33 6 27 5 81 5.68 5.07 4.90 4.71 4.63 4.41 4.34 4.30 4.20 3.82 3 76 3 68 3 62 3 58 3.52 3 47 3.34 3 29
33 21 43 58 17 16 18 11 35 15 15 11 35 14 19 15 28 12 51 13 28 100 26 12 30 30 10
6.21 4 54 4 26 4 01 3.61 3.44 3.30 3.19 3.10 2.97 2.90 2.85 2.83 2.71 2.62 2.50 2 47 2 42
8 39 6 17 2 2 2 35 38 4 2 3 4 4 100 13 3 9
4
2 5 8 11
Z n N H a P O dB 6.33 5.12 4.81 4.62 4.34 4.08 3.93 3.50 3.37 3 24 3.16 2 77 2.72
9.04 5.60 4.81 4.60 4.52 4.34 4.16 3.80 3.68 3.59 3.40 3.35 3.12 3.01 2.95 2.90 2.81 2.74 2.70 2.59 2.53 2.51
I d, A. Zn2KH( PO4)2 100 2.42 96 2.35 3 2.31 12 2.26 14 2.22 18 2.20 72 2.18 16 2.08 26 2.04 7 1.958 12 1.945 2 1.875 26 1.852 10 1.842 12 1.810 10 1.764 16 1 725 14 1.700
3.25 3 22 3.17 3.12 2.93 2 91 2.85 2.81 2.79 2,72 2 69 2.68 2.65 2.63 2.61 2.44 2.38 2.32 2.18 2.15 2.10 2 05 2.04 1.989 1.9.50 1.895 1,767
30 28 11 42 19 17 91 10 32 13 14 14 10 38 25 14 12 10 11 19 10 10 11 19 14 11 17
Zn KPOi 2.23 2.19 2.13 2.00 1.927 1.882 1.816 1.795 1.774 1.715 1.682 1.652 1.601 1.591 1 525 1.514 1 469
2 9 4
8 3 6 2 2 4 3 11 2 5 12 4 20 4
Zn(n”d)pHd( PyO,)?.2 H 2 0 7.30 6.63 5.96 5.57 4.93
100 24 13 29 6
NO. 5 , S E P T . - O C T .
2.786 2.753 2.657 2,635 2.593
1966
527
12 4 6 3
11
Table 111. d, A.
Continued d, A.
I
I
z n (XH4),H4( P207)2.2H20 4.79 4.38 4.27 3.65 3.53 3.46 3.31 3.19 3 15 3 06 3 03 2.976 2.859 2.812
88
5 6
55 16 35 6 18 10 14 14 8 6 6
2.564 2.536 2 471 2.395 2.354 2,325 2.238 2.205 2 174 2 137 2 099 2 072 1.886 1.809
4 3 6 11 4 2 2
5 3 4 7 6 5 3
Zn(NH4)dP20i)e. 6H20 9.19 8.84 8.70 7.84 6.54 6.31 6.19 5.43 5.33 4.63 4 47 4 35 4 07 4.04 3.96 3.91 3.51 3.35 3 32
10 21 100 83 47 10 41 9 38 h
7 34 7 11 13 10 53 24 52
3.28 3.22 3.16 3 11 3 05 3.00 2 93 2,78 2.70 2~-59 2 29 2 28 2 19 2.18 2.17 1 959 1 931 1 814 1.610
7 14
-
24 13 30 39 43
-
8 7 15 13 11 10 7 7 16 11
Zn(NH4)2P207.H20 14.24 9.20 7.14 5,68 4.75 4.71 4.50 4.23 4.16
8 6 100 1 9 9 4 3 4
2.77 2.67 2.63
7 2 2
2.53 2.47 2.43 2.39 2.25 2.20 2.16 2.12 2.08
2 2 3 1 3 1 1 1 2
1.618 1.592
1 1
Zn3(NH4)?(P207)2.2Hn0 9.20 6.10 5.40 4.83 4.42 4.09 4.00 3.90 3.84 3.58 3.48 3.37 3.28 3.00 2.88 2.81 2.70 2.64 2.612 2.479 2.453 2.415 2,342 2.291
528
100 10 23 23 21 2 6 12 28 6 41 23 44 48 6 33 6 16 17 12 15 6 4 30
2.244 2,222 2.137 2.039 2.009 1.961 1.937 1,894 1.870 1.843 1.826 1.794 1.773 1.700 1.679 1,663 1 ,642 1.579 1.548 1.537 1.521 1.504 1.465 1.440
7 8 6 17 6 6 12 2 4 2 7 7 3 9 5 9 2 6 9 8 7 8 5 8
J. A G R . F O O D C H E M .
ever, behaves much as the other divalent cations and precipitates over a wide p H range as Mn(NH4)2P20i,2H20, or enters into isomorphous substitution with the divalent metal cation [Fe(II), Zn? C u ] in other precipitates. lron and Aluminum Salts
Iron and aluminum are quite soluble in merchant-grade acids ( 9 ) , and these metals are never completely precipitated as sludge, even in clarified wet-process phosphoric acids. The amounts of iron and aluminum that remain form undesirable precipitates when the acids are ammoniated. Iron is also introduced into the \vet-process acid before and during ammoniation by the corrosive action of the acid on processing equipment. Upon ammoniation, the solubility of these metals in the acid solution decreases rapidly-presumably because of the decomposition of iron and aluminum phosphate complexes-and they precipitate as compounds that not only create a handling problem but also immobilize phosphorus in forms not readily available to crops. ‘/Vhen acids that contain only orthophosphate are ammoniated, the most common initial precipitate above pH 3 is an amorphous gel with a variable composition of about (A1,Fe)POa.nHsO in which small amounts of other metals may be substituted. O n standing in an ammoniated solution with pH 3 to 5 for a few days, the gel reacts to form crystals of (NHa,K)3AljH6(P04)8.18H20 (taranakite) and NH1Fe(HPOa)z (70, 75). O n ammoniation of the acid, to near neutrality or alkalinity, both iron and aluminum precipitate immediately as gelatinous phosphates. O n standing in the mother liquor, the iron phosphate remains unchanged, but the aluminum phosphate crystallizes in a few days as Al(NH4)zH(POa)2.4Hz0(5) a t pH 5 to 7 and as AlPJHaP040H.2H20 a t pH‘s above 7. In dilute solutions at pH’s above 7 , the crystals are mixtures of AlS H 4 P 0 4 0 H 3H20 . and the dihydrate (5). The two hydrates can be differentiated by infrared; both contain strong OH absorption bands in accord with the assigned formula. Solutions of condensed ammonium phosphates, such as TVA‘s 10-34-0 liquid fertilizer obtained by ammoniating superphosphoric acid (337, P, 757c P 2 0 5 ) ( 7 8 ) , sequester aluminum and ferric iron. In a study of this effect, samples of the 10-34-0 solution were adjusted to pH 6 or 8, and to portions of each of these was added aluminum or ferric nitrate to provide 1.57c A1 or Fe in solution. -4t pH 8, the solution containing aluminum yielded a precipitate of A1(NH.t)?P2OiOH,2H.0 after 2 weeks, but the solution containing iron yielded no precipitate in 4 years. At p H 6, the solution containing aluminum ~
yielded a precipitate after 6 months; this precipitate has not been identified. The solution containing iron started to precipitate in a few days, but 6 months were required to produce a significant amount of precipitate. Increasing the iron content of the solution did not increase the rate or the amount of precipitate proportionately. The iron precipitate is unusual in that it contains both ortho- and pyrophosphate; its formula ij Fe(NH4)3HP04PzOi. H z 0 . The corresponding anhydrous crystalline salt appears in solid ammonium polyphosphate prepared by ammoniating merchant grade or concentrated wet-process phosphoric acid under pressure a t temperatures below 240’ C. (ti). Both the anhydrous salt and its monohydrate can be prepared readily from reagent grade chemicals. Their infrared spectra show P - 0 absorption bands for both P04-3 and P207-(; those of the pyrophosphate are more intense. Chromatographic analysis showed that the distribution of the phosphorus in the anhydrous salt was 377, ortho-, 60y0 pyro-, and 3% more highly condensed phosphates, and in the monohydrate was 35% ortho-, 647, pyro-, and lY0 more highly condensed phosphates. Only two other mixed ortho- and pyrophosphates have been reported in the literatureK.gH?(P04)?P207 (73) and K5H2P04P20i (77). Both Fe(T\1”4)3HP04P20i and its monohydrate are soluble in dilute mineral acid and neutral ammonium citrate solution. When ammonium polyphosphate is prepared at temperatures above 240’ C., a series of acid-insoluble salts with the composition of (Fe,.41)KHaP20, is formed, frequently as a scalar deposit on the walls of the reaction vessel. The potassium analog, (Fe,A1)KP20i, is formed during the production of potassium polyphosphate by heating a mixture of potassium chloride and wet-process phosphoric acid, or when potassium is added to ammonium plyphosphate ; it also is insoluble in acid. The behavior of ferrous iron in ammonium polyphosphate solutions is similar to that of zinc and divalent manganese. At p H 6>ferrous iron precipitates in t\vo forms. The more common form is Fe(SH4)2P.10i. 2H20, a graygreen precipitate that oxidizes and turns brown on exposure to the atmosphere. This salt is formed rapidly when metallic iron is attacked by the fertilizer solution. .4 similar salt in which potassium substituted for part of the ammonium was found as a product of the corrosion of a mild steel container in jvhich an ammonium polyphosphate solution containing potassium had been stored. -4less common ferrous compound that is formed in the same solutions is Fe(NHJ6(P2Oi)2.6H?O. The amount of this compound increases as the concentration of the solution is increased and
the ratio of pyro- to orthophosphate is increased much abov- 1.
Discussion Some of the metallic phosphates that appear in products of the ammoniation of merchant grade and concentrated wet-process phosphoric acids were identified and characterized. bfost of the compounds are pyrophosphates of the metallic impurities that were in solution in the original acid, but some are phosphates of micronutrient metals that are added to the fertilizers. Some of the compounds have been reported previously 170, 72, 74, 75), but their descriptions were incomplete. These compounds precipitate a.s sludges that interfere \vith the handling of the fertilizer solutions. and some of the compounds immobilize phosphoi:us in forms that are of relatively little agronomic value. Isomorphous substitution is common among these compounds--potassium for ammonium, aluminum for ferric iron, and Fe(I1). h l n ( I I ) , Zn, and Cu for each other. These. substitutions and those in series such as (MnjFe)(NH4)2P2Oi. 2H20 and (Zn,blg.Fe)(NH?),{P?Oi)2 , 6HZO cause: only small changes i n position or intensity of the x-ray reflections. LIsually there are no changes in crystal morphology or habit, but there a r e regular changes in rhe refractive indices with change:, in chemical con,stituents. The most common precipitates in liquid fertilizers made by ammoniating wet-process phosphoric acids are those of magnesium, iron, and aluminum. \\''hen the solutions conta.in only orthophosphate, struvite and gelatinous iron and aluminum phosphates form readily; when the solutions contain condensed phosphates, the dimorphs of Mg(NH4) 2PyO;,4H?O are usually precipitated. T h e impurities most commonly found in solid ammonium and potassium poly-
Literature Cited
(3) Frazier, A. W., Lehr, J. R.? Smith, J. P., Am. Mineralogist 48, 635 (1963). (4) Frazier, A. \V.: Lehr, J. R.. Smith, J. P . , J. AGR. FOOD CHEW 12, 198 (1964). (5) Frazier, A. W.>Taylor, A. W., Soil Sci.SOC.,4772. Proc. 29, 545 (1965). (6) Getsinger, J. G., Siegel, M. R., M a n n , H. C., Jr., J. AGR. FOOD CHEM.10, 341 (1962). (7) Haseman, J. F., Lehr, J. R . , Smith, J. P., Soil Sci. SOL..Im. Proc. 15, 76 (1951). (8) Larsen, E. S.,Berman, H . , L7. S. Geol. S u r u q Bull. 848 (1943). (9) Lehr, J. R., Fraziei->A . W.,Smith, J. P., J. .\GR. FOOD CHEM.14, 27 (1966). (10) Lindsay, W. L., Frazier, A. \I7., Stephenson, H. F.. Soil. Sci. SOL.Am. Proc. 26,446 (1962). (11) McCullough? J. F.. Hatfield. J. D., "Solubility of Zinc Pyrophosphate in Ammonium Pyrophosphate Solutions." 150th Meeting, ACS, Atlantic City, N. J., September 1965. (12) Palache, C., Berman, H., Frondel, C., "Dana's System of Mineralogy," V-01.11, pp. 699-700, Wiley, New York, 1951. (13) Silber, P.. Brun, G., Compt. Rend. 256,4223 (1963). (14) Taylor. A . \V.; Frazier, A . L\r., Gurney, E. L.. Trans. Faraday Sod. 59, 1580 (1963). (15) Taylor, ,4. \\'.%Gurney, E. L., Frazier. A. \V., Soil Sci. Soc. Am. Proc. 29, 317 (1965). (16) Terman, G. L.. unpublished T1.A data. Muscle Shoals, Ala., 1965. (17) \'erdier, J.-M.. D o r h i e u x - M o r i n , C., Boullt, A , : Compt. Rend. 257, 917 (1963). (18) M'ilbanks. J. .4., Xason? M. C., Scott, TV. C.. J. XGR. FOOD CHEM. 9, 174 (1961).
(1) Broivn, E. H.? Lehr, J. R.. Frazier, A. W.,Smith, J. P., J. ACR. FOOD CHEM.12,70 (1964). (2) Brown, E. H., Lehr, J. R., Smith, J. P.: Frazier, A. \V.. Ibid.. 11, 214 (1963).
Received for review January 21, 1966. Accepted April 28, 1966. Division of Fertilizer and Soil Chemistry, 752nd itleetinf ACS, ,vew Yoi'ork, .X7. Y., September 1966.
phosphates are (Fe,Al)(NH4)3HP04P207, (Fe ,Al)N H 4P 2 0 7 , and (Fe,AI) K P 2 0 7 , Two of the most common precipitates cause the most difficulty in identifying the solids. Ferrous iron precipitates as Fe(NH4,K)?PrO,.2H2O in the form of poorly developed, complex blade-crystal aggregates which decompose rapidly on exposure to air because of oxidation of the ferrous iron. The crystallographic data for this salt are only approximate; its x-ray pattern was weak and diffuse. The manganous analog hln(NH4)2P?0 7 . 2 H a 0 is much like the ferrous salt. T h e amorphous iron and aluminum phosphates (Fe,A1)P04.nHzO do not have characteristic x-ray patterns; they are optically isotropic with refractive indices in the range 1.48 to 1.64. The refractive index varies widely with such factors as the amount of adsorbed water. the ratio of iron to aluminum, and the amount of foreign cations that has been coprecipitated, occluded, or adsorbed. Micronutrient cations added to phosphate fertilizers as soluble salts usually precipitate slowly over a long time as compounds which are quite stable in the fertilizer's environment. In liquid fertilizers: these precipitations adversely alter the composition of the frrtilizer and concentrate the micronutrient elements in the solid phase. \\'hen the fertilizers are applied to the soil, these compounds will control the rates at which the micronutrients are released to the plants. Further studies are being made of the agronomic value of many of these compounds and the conditions that control their formation.
V 0 L. 1 4, N 0. 5 , S E P T.-0 CT. 1 9 6 6
529
